Marketing, availability, and use of electronic nicotine delivery systems (e-cigarettes) are growing at an exponential rate, particularly among young adults. E-cigarettes may be a form of harm reduction for cigarette smokers, potentially helping to reduce the largest preventable cause of death in the United States. It is critical that we understand as much as possible about why cigarette smokers do or do not choose to use e-cigarettes. Additionally, e-cigarettes are a new entryway into nicotine use for non-smokers. E-cigarettes often contain addictive and toxic chemicals and could potentially renormalize cigarette smoking. It is imperative we understand what is driving usage or lack of usage among young adults including both smokers and non- smokers. Drug outcomes expectancies, i.e., beliefs about the results of drug use, are a key tool in predicting substance use initiation. Drug expectancies can be understood as information structures in long-term memory that organize input to the central nervous system and guide management of behavior, acting as a final common pathway implicated in connections between prior conditions and drug use decisions. Before substance use, drug expectancies develop from observation via family members, peers, and the media. After use initiation and during continued use, expectancies tend to become stronger, more associated with other elements in long-term memory, more specific, and more positive. Drug expectancies have been found to be robust predictors of substance use initiation. We propose using a mixed-methods approach to develop an e-cigarette expectancy questionnaire. Test development will involve two phases. In the first formative phase, focus groups with young adults (N=80, stratified to include equal numbers of e-cigarette users, i.e., vapers, non-vapers, smokers, and non-smokers) and consultation with an expert panel will be used to develop an initial item bank. In the second phase, this initial item bank will be presented to a large sample of young adults (N=500). Item Response Theory will be utilized to determine the best functioning items and to create a shorter survey. This survey will be assessed for its convergent validity. The end result will be a well-informed, psychometrically valid assessment of e-cigarette expectancies. This outcome expectancy measure for e-cigarettes will facilitate future research and help guide development and evaluation of public health interventions, such as marketing regulations, labeling requirements, and development of counter-messaging.